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Drivers of trends and regime shifts in ocean phytoplankton and zooplankton

Final Report Summary - TROPHYZ (Drivers of trends and regime shifts in ocean phytoplankton and zooplankton)

Final report summary: Drivers of trends and regime shifts in ocean phytoplankton and zooplankton (TROPHYZ)

Long-term changes in marine primary productivity is the largest uncertainty in predicting future changes in fisheries and marine ecosystems. Therefore, assessing climate change impacts on primary productivity has become a priority. The presence, magnitude, and even direction of changes in phytoplankton abundance over the past few decades are still debated in the literature. This is primarily due to differences in the datasets/methodologies used, and challenged by the presence of large natural variability. Changes can manifest either as smooth long-term changes or abrupt changes, and can be induced by environmental forcing (bottom-up), predation (top-down) or generated from the presence of memory in the system. Distinguishing these different modes of change and variability is crucial towards better understanding their drivers, and requires state-of-the-art statistical approaches. This project aims to investigate the presence of trends, abrupt changes and thresholds in ocean phytoplankton and zooplankton abundance and identify the mechanisms responsible for those changes by connecting statistical approaches to marine ecosystem biology and physics.
The project had four key objectives: 1) identify which marine ecosystems are exhibiting change in plankton abundance, 2) quantify change and uncertainty in plankton abundance, 3) identify the mechanisms responsible for the changes and 4) evaluate our potential to predict abrupt changes in phytoplankton and zooplankton abundance. In light of objectives 1 and 2, new statistical development enabled distinguishing marine ecosystem abrupt changes from long-term changes and environmental noise. Further development also allowed distinguishing abrupt changes from long-memory in the system. The change-point methodology developed in this project was used to investigate two key marine ecosystems that have been suggested to undergo abrupt changes in the past: North Pacific and North Atlantic. At the broader scale, we have also produced new estimates of chlorophyll (a proxy for phytoplankton biomass) trends and uncertainties using satellite data and a state-of-the-art Bayesian space-time modelling approach, highlighting key regions undergoing change and also contributing to key objectives 1 and 2. With regards to key objective 3, the mechanisms responsible for the 1970s regime shift in the North Pacific were connected to extreme atmospheric events and sustained changes in the ocean-atmosphere coupling, which has been evidenced by both observations and a large ensemble from an Earth system model. In current work, we are investigating whether future extreme atmospheric events will intensify in a warming world, and assessing the potential impacts on marine ecosystems. This is important and timely, given increasing pressure on marine ecosystems and the need to prepare and mitigate for future changes. As for the North Atlantic, we find strong evidence for nonlinear stochastic dynamics in plankton time-series, illustrating the complexity of species interactions and response to environmental effects, and potential for predictability, thus also contributing to key objective 4.
My appointment as a Lecturer at the University of Southampton provided optimal conditions to increase the impact of my research, develop new collaborations in the UK, Europe and internationally and grow a productive research group. Through the duration of the grant, I have been employed through a stable position, which was confirmed on a permanent basis in 2015. New collaborations were developed at the University of Southampton in the Ocean and Earth Science and Mathematics departments, and with the National Oceanography Centre Southampton. Key collaborations also started with Lancaster University, Plymouth Marine Laboratory and SAHFOS in the UK, with IPSL in France and MIT in the USA. The financial resources provided by the grant have boosted establishment of a productive research group: two PhD students contributing to this project have now graduated and are employed as researchers at the University of Cambridge and the National Oceanography Centre Southampton, and I am still currently training three PhD students (one of whom was funded by this project). The grant also helped me to leverage additional funding at the institutional, industrial and national levels to support my research group. Through the duration of the grant, I gave 12 invited talks and my group gave 15 contributed presentations at workshops/conferences resulting from this project. This work has led to 6 published papers (3 first-authored by my PhD students), 2 manuscripts are currently under review and 4 manuscripts are in preparation, which demonstrates increasing impact and recognition of my research and mentoring/training skills.

Email contact: c.beaulieu@soton.ac.uk

Project webpage: https://www.southampton.ac.uk/oes/research/projects/drivers-of-trends-and-regime-shifts.page